The present invention relates generally to a cylinder head for use on a spark-ignition internal combustion engine with a four-stroke and two-valve system and such spark-ignition internal combustion engine and, more particularly, to such spark-ignition internal combustion engine cylinder head and the spark-ignition internal combustion engine which provide for enhancing the output and the rotational speed of the engine and such spark-ignition internal combustion engine.
The four-stroke and two-valve type spark-ignition internal combustion engine typically comprises a cylinder head joined to a cylinder having a piston mounted therein, the cylinder head including a planar squish surface opposing the outer periphery of the top surface of the piston such that a squish area is defined between the squish surface and the piston top surface. The cylinder head is formed in its wall with a combustion chamber recess adjoining the squish surface such that the combustion chamber recess is cooperative with the piston top surface to define a combustion chamber. In addition, the cylinder head has a set of intake and exhaust ports formed open through the wall of the combustion chamber recess at the apex thereof, the intake and exhaust ports being provided with intake and exhaust valves, respectively. An ignition plug aperture is also formed open through the wall of the recess with an ignition plug protruding into the combustion chamber recess.
With the spark-ignition internal combustion engine constructed as described above, as the piston is moved up to a point near its top dead center, the air-fuel mixture is compressed in the squish area defined between the squish surface and the piston top surface whereby there is generated a squish stream swirling in the combustion chamber. The swirling air-fuel mixture moves upwardly in the combustion chamber to be ignited by the ignition plug, and the ignited air-fuel mixture then burns with its flame front propagating in the combustion chamber, so that the piston is moved down toward its bottom dead center by the expansion of the burning air-fuel mixture.
However, in the conventional spark-ignition internal combustion engine described above, both of the squish surface of the cylinder head and the piston top surface which together define the squish area are formed planar and the squish area is located below the projecting lower end of the ignition plug. Due to this arrangement, the squish flow as produced by the squish area may not move directly toward the ignition plug located above squish area, but swirls around in the combustion chamber before it is directed to the vicinity of the ignition plug. Consequently, the squish flow was not capable of guiding an adequate amount of the air-fuel mixture to the vicinity of the ignition plug, and therefore had the disadvantage of being unable to enhance the propagation rate of the flame front of the ignited air-fuel mixture (which will be referred to as flame propagation rate hereinafter. As a result, such prior art construction undesirably led to a decrease in the output and the rotational speed of the internal combustion engine.
In order to overcome the foregoing problems, this invention contemplates to provide a cylinder head for a four-stroke and two-valve spark-ignition internal combustion engine and such spark-ignition internal combustion engine which provides for enhancing the output and the rotational speed of the engine by increasing the flame propagation rate of the ignited and burning air-fuel mixture.
In order to accomplish this object, the cylinder head for a spark-ignition internal combustion engine as set forth in claim 1 is designed to be used on a four-stroke and two-valve spark-ignition internal combustion engine, and is adapted to be joined at mating surfaces to a cylinder having a piston mounted therein. The cylinder head includes a generally planar squish surface opposing the outer peripheral portion of the top surface of the piston; a combustion chamber recess formed in the wall of the cylinder head adjacent the squish surface and defining together with the piston top surface a combustion chamber; a set of intake port and exhaust port formed open through the wall of the combustion chamber recess either at the apex thereof or on the lateral side of the combustion chamber recess opposite from the squish surface; an ignition plug aperture formed open through the wall of the combustion chamber recess at a location closer to the squish surface relative to the intake port and exhaust port and adapted to receive an ignition plug extending therethrough into the combustion chamber; and a squish guide groove formed by notching into the wall of the combustion chamber recess so as to extend from the side of the ignition plug aperture to a location of the squish surface adjacent the inner wall of the cylinder.
The spark-ignition internal combustion engine as set forth in claim 2 is a four-stroke and two-valve type spark-ignition internal combustion engine and comprises a cylinder having a piston mounted therein; a cylinder head adapted to be joined at mating surfaces to the cylinder; a generally planar squish surface formed on the wall of the cylinder head adjacent the mating surfaces and opposing the outer peripheral portion of the top surface of the piston; a combustion chamber recess formed in the wall of the cylinder head adjacent the squish surface and defining together with the piston top surface a combustion chamber; a set of intake valve and exhaust valve disposed on the wall of the combustion chamber recess either at the apex thereof or on the lateral side of the combustion chamber recess opposite from the squish surface; an ignition plug through the wall of the combustion chamber recess into the combustion chamber at a location closer to the squish surface relative to the intake valve and exhaust valve; and a squish guide groove formed by notching into the wall of the combustion chamber recess so as to extend from the side of the ignition plug to a location of the squish surface adjacent the inner wall of the cylinder.
With the spark-ignition internal combustion engine cylinder head or the spark-ignition internal combustion engine according to the present invention, the cylinder head is joined to a cylinder block at mating surfaces. In use, upon the intake port being opened by the intake valve, the piston is lowered toward its bottom dead center as the air-fuel mixture flows into the combustion chamber. When the piston reaches its bottom dead center, the intake port is closed by the intake valve and the piston is moved up toward its top dead center while the air-fuel mixture in the combustion chamber is compressed by the rising piston, whereby squish flow is produced between the outer periphery of the piston top surface and the squish surface with the compression of the air-fuel mixture.
The thus created squish flow ensures adequate mixing of the air and fuel of the air-fuel mixture. The air-fuel mixture is ignited by the ignition plug and begins the combustion during the process while the piston rises toward its top dead center. With the piston rising, the air-fuel mixture over the squish surface is caused to pass around the ignition plug aperture (ignition plug) and flow into the central region of the combustion chamber under the guidance of the squish guide groove and ignition is effected on such flowing air-fuel mixture.